Let us prove that \(\lbrace  \sin z_n t\rbrace _{n \ge 1}\)  is a Riesz basis; for \(\lbrace  1\rbrace  \cup \lbrace  \cos z_n t\rbrace _{n \ge 1}\)  the proof is analogous.
According to Proposition 1.8.5 from [1]}, it is sufficient to prove the completeness of the system \(\lbrace  \sin z_n t\rbrace _{n \ge 1}.\)
